ipmi:ssif: Remove dynamic platform device handing

Platform devices can only come in through the DMI interface, and that
will get done before initialization is complete.  Therefore there is no
reason to hande getting a device in new_ssif_client after
initialization.

Dynamic entries can still come in through the i2c interfaces, but that's
handled differently.

Signed-off-by: Corey Minyard <cminyard@mvista.com>